The problem of resolving two point sources has been intensively studied as model problem for optical system resolution characterisation for more then a century. For a long time only visual observation of the light coming from the sources was available, thus resolving criteria were based on visual characteristics of intensity distribution [1]}, [2]}. Visual criteria, such as Rayleigh criterion, were aimed to distinguish between images of two sources and one, but not to describe the problem of the separation estimation.
